要 旨 ：
This seminar will review resent experimental observations and their
theoretical modeling in charge density waves (CDW). The results may be
relevant to a broad class of low dimensional electronic systems with
symmetry broken states ? the nearest extension is the ferroelectric
charge ordering in organic conductors. The selected observations will be
related to strong, topologically nontrivial perturbations of the order
parameter under an external impact. The pattern may be static, induced
by electric field or dynamic, under the optical pumping ? these are the
two new trends in solid state physics [1].
Recent optical study of a far-from-equilibrium CDW recovered coherent
aperiodic undulations of the order parameter, critical slowing down of
the collective mode, and evolution of the particle-hole gap. Numerical
modeling allowed interpreting the observations, particularly the
spatio-temporal distortions arising from “earthquakes” - annihilation
events of topological defects in depth of the sample.
Strong perturbations were also found at the microscopic scale accessed
by the STM; there are the amplitude solitons expected to play a role of
neutral spin carriers - spinons.
Experiments on nano-junctions in CDWs indicate on the intrinsic
reconstruction by creating stationary and transient electronic vortices ?
dislocations. The modeling shows that vortices are formed stepwise in
the junction when the voltage across, or the current through, exceed a
threshold. The vortex core concentrates the total voltage drop, working
as a self-tuned microscopic tunnelling junction.
[1] http://lptms.u-psud.fr/impact2012/